Rare earth and magnetic materials
Today we mainly introduce rare earth and magnetic materials, mainly rare earth. Rare earth related topics are very broad. We will focus on magnetic materials to introduce why rare earth is important and its significance.
Rare earth is an important strategic resource
Table of Contents
- Rare earth is an important strategic resource
- How about rare earth in China?
- Challenges to the sustainable development of China’s rare earth industry
- Now what are we going to solve?
- Rare earth magnetic (permanent magnet) materials and their applications
- Permanent magnet motor and other applications (magnet assembly)
- Rare earth high frequency magnetic materials and their applications
- Magnetic refrigeration materials and technology
- Why magnetic refrigeration?
Rare earth is called “strategic resource”, while magnetism and rare earth are inseparable, and 40% of the uses of rare earth are related to magnetism.
When it comes to magnetism, we know that any matter has magnetism, and there is a magnetic field in every space. From the magnetic field of the brain to the magnetic field of the neutron star in space, their intensity is 10 ^ 30 times different. Magnetism involves a wide range of fields. I am engaged in the study of condensed matter physics. Almost all fields involved in condensed matter are related to magnetism. From the perspective of application, the wide application of magnetic materials and magnetic technology is related to our industry, agriculture and national defense.
Magnetism is a very old subject. So far, there are 216 Nobel Prize winners in Physics (up to 2020), of which 32 are related to magnetism. To talk about rare earth, I want to focus on the physical properties of rare earth elements and iron group elements, so as to discuss the importance of rare earth.
As we all know, rare earth is a non renewable strategic resource. Some people say that they are “vitamins” of modern industry. In the 21st century, rare earth related industries are developing very rapidly, and rare earth is widely used. Rare earth elements are closely related to magnetic, optical, electrical and other physical and chemical properties. And some of its unique properties are widely used in aerospace, new energy, rail transit and many other fields and industries. What is particularly important is that rare earth resources will become a focus in Sino US and Sino EU relations, mainly because they have key links with defense applications such as missiles, radars, submarines and satellites.
Now the problem we are facing is: Although we are rich in rare earth resources, when we really want to do rare earth application, we export rare earth instead, and in the end, some technologies will be stuck by Europe and America. From the general secretary to our grassroots researchers, we have always attached great importance to this issue and want to change the status quo. In 2019, when the general secretary visited Ganzhou, he said that rare earth is an important strategic resource, which is non renewable. It is necessary to continuously improve the level of R & D, extend the industrial chain and increase the added value.
Due to the wide connection of rare earth, the United States, Japan and the European Union all regard rare earth as the core of resource competition, especially the United States, which has constantly issued some strategic reports. Some important research reports and lists are related to rare earth. They want to not use their own, use other people’s, and get stuck in other people’s necks.
How about rare earth in China?
As we all know, our country is rich in rare earth resources and plays an important role in the world. In the early days, people always said that rare earth is a trump card of our country. They said that if we have rare earth, can we use rare earth to counter China US confrontation. I don’t think it’s possible, because rare earth resources account for more of the total.
In the early days, we thought our rare earth reserves were very large, but in fact, in 2012, China issued a white paper on rare earth status, which mentioned that China’s rare earth reserves accounted for 23% of the world’s in 2009. The United States also has a lot of rare earth resources. After a long time of efforts, the output, export and consumption of rare earth are all the first in the world. Is that good for us? Actually, it’s not good at all. We provide 90% of the world’s market supply with 23% of our reserves, which is equivalent to selling rare earth resources.
I particularly feel that this situation needs to be changed. In the 1950s and 1960s, especially after the 1960s, the long-term accumulation in mining, smelting and separation of rare earth made our country have an absolute advantage in these aspects and a right to speak. But we mainly sell raw materials to others.
There are rare earth deposits in more than 70 countries in the world, and there are nearly 800 rare earth deposits in the world. China accounts for a relatively large proportion. Do you still think rare earth is too rare? In fact, rare earth is not rare at all, and its reserves are very rich.
The discoverer of rare earth in China should be Mr. Ding Daoheng. In 1927, he organized a Northwest Expedition to China and Europe and discovered iron ore. Later, an ore called monazite was found in the iron ore. Since then, rare earths in our country have gradually been discovered. From the discovery to later application, the well-known Bayan Obo rare earth deposit, located in Baotou, was formed. It can almost be said that the vast majority of rare earths in the world are supplied by the Bayan Obo mine in Baotou.
For rare earth mineral resources and raw materials, please look at the picture above. In the early days, people didn’t pay much attention to it. Until the 1960s, Americans paid special attention to it. After the discovery and utilization of Bayan Obo mine in China, with the improvement of our purification and smelting level, Bayan Obo mine has occupied a very large share and discourse power in the world. But for quite a long period of time since then, up to around 2000, it was basically based on resources: utilization and exploitation there.
The distribution of rare earth in China is characterized by “heavy in the South and light in the north”: light rare earth in the north and heavy rare earth in the south. The so-called light rare earths are lanthanum, cerium, praseodymium and neodymium. Baiyunebo, Weishan in Shandong and Mianning in Sichuan are mainly light rare earth elements. The five southern provinces, also known as six or more, are dominated by heavy rare earths. Gadolinium, terbium, dysprosium, samarium, and holmium, erbium, thulium in the periodic table are all heavy rare earth elements. Heavy rare earth is ionic rare earth, which is not a mine in fact. The current mining method is different from the light rare earth mining in the north, causing many environmental problems.
Although China’s rare earth resources are mainly concentrated in Baotou, Shandong and Sichuan in the north and several places in the south, they are distributed in 22 provinces and regions in China.
Bayan Obo mine is the largest rare earth mine, accounting for 83% of the total rare earth reserves in China. But many minerals are symbiotic. The iron content here is very high, and the proportion is very large. Rare earth generally accounts for only about 6% to 7%, less than 3% in Liangshan of Sichuan, and less than 8% in Weishan of Shandong. In addition, the southern ionic type of medium and heavy rare earths account for about 3%. However, despite the low content of heavy rare earth in the south, it is very important in the world. Because the medium and heavy rare earth, especially the heavy rare earth, plays a key role in the application, especially in some key strategic applications. Although the amount is relatively small, its importance is more important than other elements.
In a rare earth ore, the distribution of rare earth elements is uneven and associated with iron and niobium. Rare earth has 17 elements, many of which are mixed together. For example, in Baotou ore, lanthanum and cerium account for almost 3 / 4, while other elements, including heavy rare earth, account for only 1 / 4. However, in the south, heavy rare earths are especially abundant.
Sometimes, as many as 70 elements are mixed up. Before our mining utilization rate is very low, mainly from the iron.
We know that there is a Baotou Iron and steel company in Baotou, which makes iron from rare earth ore. In the early days of ironmaking, because we didn’t know much about it at that time, we threw a lot of rare earths in the tailings. Now we attach importance to it.
If we say comprehensive utilization, more than 70 elements are very important. In addition to rare earths, niobium, titanium, zirconium and, of course, radioactive thorium can play a role in many fields if they are all used. In the end, we can even make glass ceramics from waste residue that we no longer think is valuable. It can be used in electric power, chemical industry, construction, metallurgy and other fields. So rare earth mineral resources are a treasure, all its elements can be well applied, play an important role in our country’s economic construction, and play a key core role in the national defense construction.
Challenges to the sustainable development of China’s rare earth industry
Rare earth is so important, but we are facing great challenges.
On the one hand, the total recovery rate is still relatively low, the present technology ecological damage is still relatively serious, and the pollution is relatively large. If you visit the north and dig out rare earth from a mine, it’s better. Mining rare earth in the south is to dig a pit on the top of the mountain, pour the acid down, and then pick up rare earth at the bottom of the mountain. The damage to the ecological environment is very serious, so our export of resources has paid a great ecological price in the early stage.
On the other hand, the comprehensive utilization level of resources is not high. As I said just now, there are so many elements, many of which are not utilized. Rare earth is not well utilized, and some other elements are still thrown into the tailings. Of course, our biggest problem is the lack of high-end products and the low added value of products. Rare earths are sold to Japan, the United States and Europe. They have developed back-end technologies, some of which are better than us. This is a serious problem we are facing.
In terms of rare earth resources in our country, we are in the lead, there are many environmental problems, and the application is relatively backward on the whole.
Now what are we going to solve?
Starting from raw materials, mining, beneficiation, smelting and separation of rare earth raw materials are the most basic needs. Then we use raw materials to make new materials, such as magnetism, optics, catalysis and so on, which will increase a little bit and increase the value. And then make the material into components, and then to the terminal application. Our ultimate goal is to move towards terminal applications. In order to do such a good job, the Chinese Academy of Sciences will build a rare earth Research Institute in Ganzhou, Jiangxi Province.
Rare earth is so important from the perspective of resources, but there are many problems. How to make good use of resources, make materials better and apply them better? What important fields are involved in it? Starting from my own professional field, I will give a few examples, mainly about rare earth magnetism, especially permanent magnetism.
Rare earth magnetic (permanent magnet) materials and their applications
Rare earth elements have some unique characteristics, which are related to their electronic configuration, energy level, spin orbit coupling, magnetic moment, and the combination of rare earth elements and transition group elements. Some properties produce unique effects.
According to some of its characteristics, many special materials can be produced, such as amorphous materials, materials with stable structure, retractable materials, materials for refrigeration, and microwave absorbing materials used in the information industry. We call it “rare earth magnetic material”.
From a functional point of view, such materials can be used for energy storage and exchange, such as mechanical energy and electrical energy conversion, magnetic energy and thermal energy conversion, and information storage and transmission. Especially in the aspect of information storage, that is, magnetic storage, so far the consumption is very large, and 70% of the stored information in the world is stored by magnetic storage. The hard disk in our computer is a typical example. It can also be used to make materials with high frequency performance, which will be discussed later.
In terms of application, it is directly related to energy, especially clean energy and efficient power (we call it magnetic power), satellite communication, unmanned machinery, urban and rural health care, solid-state refrigeration and so on.
Of all the magnetic materials, what is the most used? It’s permanent magnet material. A piece of magnet that we children take is a kind of permanent magnet material. Of course, there are also permanent magnetic materials in nature, such as ferric oxide. But if rare earth is used, the performance of permanent magnet can be very good. This kind of material is not used for sucking, it has a wide range of uses. So far, in the application of rare earth, new materials account for more than 60%, and permanent magnet accounts for more than 60% of the application in new materials. So when it comes to the application of rare earth, we say that 40% of the rare earth mined out is used as permanent magnet materials.
We are a large rare earth permanent magnet country. Originally, our level was very low, but up to now, we have accounted for 85% of the world’s total output. Some people think that we need more. In such a large output, we used to focus on the middle and low end. Now we have turned to the high-end fields of high-end cars, electronic steering, MRI and so on. Even the magnets we made are now supplied to some very important fields in the United States, including some of their core fields. Now we think that our country is already a big country in the production, processing and export of rare earth permanent magnets, but we are not a powerful country in this field.
In the field of permanent magnet materials, we have two development directions: one is to continue to improve the performance; the other is to make efficient and balanced use of various elements, especially the low-cost lanthanum and cerium, so as to greatly improve the application efficiency of rare earth resources, and finally achieve sustainable development.
Rare earth magnetic materials are extremely important. “Without magnetic materials, there would be no modern national defense,” because magnetic materials are used in radar, guidance, electronic warfare and ships. From the army, Navy, air force, artillery, electronic countermeasures now use information warfare, all need such materials. As can be seen from the figure below, such materials are used in American tanks and warships.
Permanent magnet motor and other applications (magnet assembly)
We should not underestimate the permanent magnet motor. Now the most widely used is the wire wrapped motor, which is much less efficient than the permanent magnet motor. If the efficiency of permanent magnet motors can be increased by three percentage points, and if all the newly added motors are permanent magnet motors, the energy saved will be equivalent to the total amount of Three Gorges power generation, which is very considerable.
Recently, we have developed a new structure of permanent magnet motor. There is no wire package in the middle of the motor, and the permanent magnet material is used completely to make the rotor or stator motor. In this way, the efficiency is improved, and the weight and volume are reduced. The highest efficiency can be more than 98%. This is very, very important. Now our country can realize such technology.
So what are the applications of this technology? For example, we all know about wind power generation. The longest leaf of a windmill we saw can even reach tens of meters to 100 meters. If the volume of permanent magnet motor is reduced, the installation cost and maintenance convenience will be very important. Especially when applied to offshore wind power generation, if the volume is reduced, especially the part of the middle permanent magnet motor, it will bring great convenience. This is the new technology now.
To run fast and far, cars, especially new energy vehicles, need permanent magnet motors as driving motors. Maybe after this technology is realized, the car will run better. Nowadays, the driving range of new energy vehicles is usually about 400 km. Can they reach 500 km or 600 km? I think it’s quite possible to apply permanent magnet technology.
There are also applications of permanent magnets for our C919 large transport aircraft, such as landing gear recovery and some moving parts.
Rail transit, it is driven by motor users. If we cancel all the packages in the future, we can use some new technologies to push the 350 km / h high-speed railway.
I know that there is an electromagnetic maglev train in Shanghai. In fact, permanent magnet can also be used for maglev. There is a school in Ganzhou, Jiangxi Province. They did an experiment, that is, suspension type magnetic levitation. Of course, they can also do orbit type magnetic levitation. They completely realized magnetic levitation with permanent magnets. Development like this uses the permanent magnet material I just mentioned.
Permanent magnets are also widely used in large scientific devices. Many magnets in China spallation neutron source in Dongguan are electromagnets. But in future construction, for example, if Beijing wants to build a spallation neutron source, they are now considering using some permanent magnets. Why? Because the power consumption of this device is very large after it is built. The annual electricity cost of a device can reach tens of millions, 100 million or even more. If some of them use permanent magnet materials, the energy cost of large scientific devices will be greatly reduced.
In addition, permanent magnet materials can also be used in medical field, which may not be known before. With permanent magnet technology used in surgery, time can be greatly saved. For example, the original surgery takes 30 minutes, and it can be completed in 10 minutes after using permanent magnet technology, and the healing is much better than the original. This kind of technology is created by our country. This picture was given to me by Professor Lu Yi of Xi’an Jiaotong University. The application of permanent magnet in medical treatment is very advanced in the world.
Rare earth high frequency magnetic materials and their applications
In addition to rare earth permanent magnet, there is another kind of material called rare earth high frequency magnetic material. This kind of material can be applied in a very high frequency band. The rare earth elements used in the permanent magnet materials I just mentioned are mainly praseodymium, neodymium, terbium and dysprosium. Just as the high-frequency magnetic materials can use yttrium, lanthanum and cerium to realize the comprehensive, balanced, efficient and economical utilization of rare earth resources. From the perspective of the use of rare earth elements, high frequency magnetic materials have great advantages in balanced utilization, efficient utilization and economical utilization.
High performance high frequency materials are mainly used in 5g communication and Internet of things. Especially when the working frequency requirements are higher and higher, and now even hope to reach about 6GHz, the performance requirements of these electronic components are also correspondingly improved. Now our mobile phones are doing very well, but most of the components still rely on imports. So whether we can use our rare earth materials to make the frequency band of these components higher is a direction of efforts. High performance high frequency materials are widely used, such as antennas, inductors, electromagnetic compatibility, absorbing materials, stealth and so on. Their market share is also very high.
Now our 5g mobile phone, its application frequency is generally about 3GHz. After that, we must make the volume smaller and the bandwidth can be increased. Why should we develop rare earth high frequency magnetic materials now? It turns out that we use ferrite as magnetic material. The working frequency of ferrite material is less than 3GHz, which is much lower than that of rare earth high frequency magnetic material. The advantage of rare earth facing anisotropic materials is high saturation magnetization and high magnetization, so the working frequency can be very high in theory. Theoretically, it can reach 20GHz, but in fact, what we have done is far from enough. But from the perspective of theoretical calculation, it can be achieved, so this is a goal we strive for.
Therefore, rare earth high-frequency magnetic materials, like permanent magnetic materials, have very important applications, and have very important strategic significance for information and communication, especially in national defense security and aerospace. In addition, the development of these materials can balance and effectively utilize our rare earth resources.
Magnetic refrigeration materials and technology
The word “refrigeration” is well-known for the fact that many materials and technologies related to refrigeration are used. Some people say that refrigeration accounts for about 5% of our country’s GDP. 5% is a very large number, which is enough to show that it covers a very wide range. Refrigeration is not only closely related to daily application, but also closely related to scientific research, industrial production, even transportation and other fields.
For example, natural gas liquefaction. As we all know, if there is only one large gas field in the “west to East Gas Transmission” project, laying pipelines is a reasonable solution, but we have a large number of gas fields, which are scattered all over the world and are not connected with each other, so the cost of laying pipelines is too high. There are also natural gas resources on the sea. If we develop natural gas on the sea, how to transport natural gas is a problem that needs to be solved. Transportation of natural gas requires liquefied natural gas, which involves refrigeration, that is, natural gas is liquefied and transported back by ship, and then reduced to gas. When we didn’t have such technology, the transportation of natural gas was a problem.
In the fields of Aerospace (we are going to build the International Space Station), military and cryogenic systems, refrigeration technology is more widely used. There is also thermonuclear fusion reactor, which also needs low-temperature refrigeration. In the medical field, the application of refrigeration technology is also very important, such as the freezing of human organs, and even the effective preservation of life at low temperature.
In the field of scientific research, a large number of our instruments need refrigeration technology, and each of our main measuring instruments basically involves low-temperature refrigeration.
Why magnetic refrigeration?
Refrigeration has such a wide range of uses. Now it is well used. Why should we develop magnetic refrigeration? Traditional refrigeration has such a problem: the working medium used will produce greenhouse effect. The refrigerant used all over the world before is called freon, which destroys the ozone layer. In theory, several agreements that our country will participate in announce that the use of Freon will be banned in the world by 2025. In the future, we will gradually reduce the use of freon as an alternative working fluid and use less and less materials with strong greenhouse effect. And we can’t stop the refrigeration. It can’t stop. For example, how to fly without refrigeration? If you don’t have refrigeration in your car or at home, you have to use an alternative method.
Magnetic refrigeration is green, energy-efficient, stable and reliable. The biggest challenge of our refrigeration system now is to solve some problems such as ozone layer destruction and greenhouse effect. In addition, the refrigeration system has to be on all day, and the air conditioner has to work all the time in summer, so we have to overcome the disadvantages of high energy consumption and high noise. If we use magnetic refrigeration, these problems will be solved very well.
But to do magnetic refrigeration, we need to use some special materials. Magnetocaloric effect was discovered very early, and a lot of research has been done. Magnetic refrigeration in low temperature environment is also very successful, so can we do room temperature magnetic refrigeration? Can we use this technology in our refrigerators and air conditioners?
In the 1970s, Americans used gadolinium as a material to achieve room temperature magnetic refrigeration. They made a prototype, but this prototype can’t be used in practice. Until about 2000, the discovery of primary phase change materials promoted the research and development of room temperature magnetic refrigeration.
General materials are second-order phase transition. After years of efforts, we have synthesized rare earth magnetic material lafesi with first-order phase transition. This is the most advantageous room temperature magnetic refrigeration material at present. This discovery has led to many research groups at home and abroad.
The above is room temperature refrigeration, and low temperature refrigeration, magnetic refrigeration also has key applications. In the field of scientific research, military, aerospace, and civil fields, there are applications or prospects.
In the low temperature refrigeration materials, we found a new material, called thulium copper aluminum. Its phase transition temperature is very low, which is the lowest one we can find in magnetic refrigeration materials so far. If such materials are used in the refrigerator, we now compound a kind of refrigerator, which achieves the lowest temperature of 3.9k when the frequency is 0.6. This is a big step forward.
The team of the Institute of physics and chemistry of the Chinese Academy of Sciences will connect it one by one, mixing working medium, pulse tube, magnetic refrigeration, adiabatic demagnetization, and the ultimate goal is to achieve 50mk. 50mk is already very low.
The main reason why we have carried out this work is that we have a goal now. Our country wants to build a gravitational wave detection equipment in the Ali Region. Ali-1 was built on the ground and is under construction. If the temperature drop is not low enough, the resolution will be affected. If we can achieve 50mk, we can improve the resolution by an order of magnitude. We can also find a way to lower the temperature a little bit, which may be able to achieve 10mk, depending on the requirements of the application platform.
In addition, the detection of space soft X-ray, our country’s proposed Hubbs satellite, also needs a low temperature of 50mk. In addition, such refrigeration devices are also needed in the field of quantum computing.
There are two main refrigeration methods, one is dilution refrigeration, the other is magnetic refrigeration, that is, one stage of adiabatic demagnetization to achieve the purpose of refrigeration. Now, we and Wuhan University of technology put forward the idea of thermoelectric and magnetic multi-function. Thermoelectric materials used to avoid magnetism. Later, it was found that if thermoelectric materials were combined with magnetic elements, they could produce a special property and improve efficiency. Is it possible to combine heat, electricity and magnetism? The magnetocaloric effect, which I just mentioned, is used to make room temperature refrigeration equipment. Magnetoelectric effect used to be used a lot, and thermoelectric effect used to be used independently. How can we connect these phenomena, that is, thermoelectromagnetism? This is a new formulation. I think it should be the direction that we need to work hard.
There is also a very important concept called “rare earth solid state refrigeration”, which is also the direction of research that needs our development. Rare earth solid state refrigeration needs to realize engineering and modularization. Once it is realized, it is expected to affect all aspects of our life.
Author: Shen Baogen
Source: China Permanent Magnet Manufacturer – www.ymagnet.com